1. Field of the Invention
The present invention relates to a brake device for a bicycle, and more particularly to a hydraulic brake device for a bicycle.
2. Description of Related Art
A conventional hydraulic brake device for a bicycle comprises a controlling unit, a hydraulic unit and a brake unit, the controlling unit comprising at least one brake cable and at least one driving axle, one end and another end of each brake cable connected to a brake lever and one end of each corresponding driving axle respectively, the hydraulic unit comprising an oil tank, at least one push stick, at least one piston, at least one elastic member and at least one oil tube, each driving axle pivotally assembled to the oil tank, one end of each push stick connected to another end of each corresponding driving axle so as to be driven by said driving axle, the oil tank having at least one receiving space so as to movably receive the at least one piston and the at least one elastic member, another end of each push stick abutted against one end of each corresponding piston, another end of each piston abutted against one end of each corresponding elastic member, another end of each elastic member abutted against an inner face of the oil tank, one end of each oil tube communicating with a lateral side of the oil tank which is adjacent to the inner face of the oil tank, the brake unit connected to another end of each oil tube, the brake unit comprising a pair of main pistons, a pair of brake pads and a brake disc, the brake disc being positioned between the two main pistons, the two main pistons communicating with another end of the oil tubes, each brake pad being defined between each corresponding main piston and the brake disc. Under this arrangement, when a rider presses the brake lever so as to pull the brake cables and drive the driving axles moving toward the brake cables; then, the push sticks are moved to push the pistons and compress the elastic members through the motion of the driving axles; thereby, a volume of oil in the oil tank flows into the main pistons via the oil tubes, so that the two main pistons move toward the brake disc; meanwhile, the two brake pads move toward the brake disc and contact with the brake disc; as a result, the bicycle is braked.
However, the conventional hydraulic brake device for a bicycle has two disadvantages as following.
Firstly, because each push stick pivots on each corresponding driving axle so as to push each corresponding piston, the piston cannot move smoothly and straightforwardly in the oil tank; as a result, the performance of the brake effect is worse.
Secondly, when the brake lever is released, the elastic members quickly bounce back to push the pistons resile; however, the oil flows slowly from the brake unit to the oil tank, so that the motion of the pistons cannot synchronize with the flow rate of the oil. Under this arrangement, if the brake device has to be actuated repeatedly, the brake effect cannot be performed completely because of the unsynchronization between the motion of the pistons and the flow rate of the oil.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional.